The present invention relates to a multiplex/demultiplex apparatus and, more particularly, to a modular multiplex/demultiplex apparatus comprising a plurality of individual module units capable of being interconnected together to provide an apparatus of variable capacity and capable of performing data multiplexing and demultiplexing operations.
In present day telephone communications systems it is well known to establish selective switching and routing connections between telephone subscribers at different locations for enabling these subscribers to communicate with each other. In one approach, groups of subscribers are assigned to corresponding trunk group modules and modems by which the groups of subscribers may be interconnected with subscribers at other locations via the associated trunk group modules and modems. In the above system configuration, data originating with subscribers at one location is generally in a parallel-bit (or demultiplexed) format and is converted to a series-bit (or multiplexed) format and routed to the trunk group modules and modems for transmission to remote subscriber equipment. Similarly, data received by the trunk group modules and modems from the remote subscriber equipment, also in a series-bit (or multiplexed) format, is converted to a parallel-bit (or demultiplexed) format and routed to the local subscriber equipment for utilization thereby.
While the abovedescribed telephone communications systems operate in a generally satisfactory manner, these systems are generally non-modular in nature and, consequently, once the assignment of subscribers to trunk groups modules and modems is established, this assignment cannot be readily and easily altered. Thus, for example, if it is desired to increase or decrease the number of subscribers assigned to a particular trunk group module and modem, this cannot be done without substantial hardware modification (and downtime) of the system. Further, once the subscriber hardware configuration is fixed, a subsequent reduction in the number of subscribers assigned to one or more of the trunk group modules and modems creates an excess-capacity situation and, if the system is not modified to reduce the subscriber hardware content, the system will still provide support or service for the unused capacity despite the fact that subscribers have been removed from and are no longer using the system. An additional disadvantage in this latter situation is that the system will continue to operate in its usual fashion during the time slots formerly used by the previous subscribers and use valuable transmission line time even though no subscriber transmissions are to take place. If it is a requirement of the system, therefore, that the transmission line be used only for actual subscriber transmissions, then the system as described above clearly would not satisfy this requirement.